Polishig fluid for metallic films and method for producing semiconductor substrate using the same

ABSTRACT

A polishing fluid for metallic films, wherein the etching rate is 10 nm/min. or less, the polishing rate under a load of 10 KPa is 200 nm/min. or more, and the contrast, a ratio of the above-mentioned polishing rate to the etching rate, is 20 or more; and a method for producing a semiconductor substrate using the same.

TECHNICAL FIELD

The present invention relates to a polishing fluid for metallic filmsused for polishing a metallic film formed on a semiconductor substrate,and to a method for producing a semiconductor substrate using saidpolishing fluid.

BACKGROUND ART

Due to the rapid progress of the LSI technique, integrated circuits tendto be scaled down and employ more the structure of multilevelinterconnection, from day to day. The introduction of multilevelinterconnection integrated circuits is an important factor aggravatingthe unevenness of the semiconductor surface which, together with thescale down of integrated circuits, promotes disconnection, reduction ofelectric capacity and occurrence of electromigration and results in thereduction of yield and reliability of the product.

Thus, a variety of processing techniques have hitherto been developedfor making flat the metallic wirings and interlayer dielectric in themultilevel interconnection substrates. One of such techniques is the CMP(chemical mechanical polishing) technique. The CMP technique isnecessary for the flattening of interlayer dielectrics, formation ofburied distribution wires, formation of plugs, etc. in the production ofsemiconductors.

CMP is carried out by rotating a carrier and a polishing padrespectively while pushing a flat wafer usually made of a semiconductormaterial, set on the carrier against the wet polishing pad under aconstant pressure. At this time, a polishing fluid introduced betweenthe wafer and the polishing pad progresses the polishing of wirings andconvexities of dielectrics mainly by way of the mechanical polishingaction, accompanied by some chemical action to achieve the desiredflattening.

There have hitherto been made a number of proposals using variouspolishing fluids and polishing methods for polishing metallic film insemiconductor substrates. As in Toshiro Doi, et al.: “CMP Technique inthe Flattening of Semiconductors” Page 235, July 1998, published byKogyo Chosakai, in the CMP of a metallic film, an oxidant present in apolishing fluid chemically oxidizes the surface of the metallic film andconverts it into a passive state and lowers the pH value to be in theacidic region to cause slight corrosion of the metal (etching). Undersuch a condition, mechanical polishing is carried out by a polishing padand abrasive grains. For instance, as polishing fluids for metallicfilms composed of aluminum or the like formed on a semiconductorsubstrate, polishing fluid obtained by dispersing aluminum oxide asabrasive grains in an aqueous solution of nitric acid having a pH valueof 3 or less (U.S. Pat. No. 4,702,792), polishing fluid obtained bymixing abrasive grains composed of aluminum oxide or silicon dioxidewith an acidic aqueous solution of sulfuric acid, nitric acid, aceticacid or the like (U.S. Pat. No. 4,944,836), etc. can be referred to.Among such polishing fluids, polishing fluids prepared by using aluminumoxide or silicon dioxide as abrasive grains and dispersing the abrasivegrains in a solution of oxidant such as hydrogen peroxide and the like,such as the one obtained by dispersing aluminum oxide in an aqueoussolution of hydrogen peroxide and phosphoric acid (U.S. Pat. No.5,209,816) are usually and widely used. When aluminum oxide is used asan abrasive grain for flattening a metallic film on a semiconductorsubstrate, however, the α-form of aluminum oxide is disadvantageous inthat defects such as microscratches, orange peel and the like may appearon the surface of a metallic film or dielectric, even though it shows ahigh polishing rate. On the other hand, when the γ-form of aluminumoxide, amorphous alumina or silicon dioxide is used as the abrasivegrains, a sufficient polishing rate cannot be achieved upon polishing ametallic film even though the appearance of defects such asmicroscratches and orange peel on the surface of a metallic film ordielectric can be suppressed. As above, polishing fluids prepared bydispersing abrasive grains composed of a metallic oxide such as aluminumoxide, silicon dioxide or the like in an aqueous solution have a problemof surface scratches caused by the low dispersibility of the abrasivegrain itself. In addition to the above, there are various practicalproblems, such as dishing (a phenomenon that the central part of ametallic film is excessively polished as compared with the peripheralpart as seen in 4 of FIG. 1D) and the generation of defects such aspits, voids or the like, etc., due to an excessive progress of wetetching, in the cases where a liquid oxidant, such as hydrogen peroxide,or a metallic etchant, such as ammonium persulfate or the like is used(JP-A-6-313164).

With the aim of overcoming these disadvantages, methods in which achemical reagent capable of forming a protective film on the surface ofmetallic film, such as an anticorrosive agent, chelating agent or thelike, is added to the polishing fluid have been proposed (JP-A-8-83780,JP-A-11-195628). However, although such chelating agent can suppress theetching and prevent the occurrence of dishing, etc., it causes a problemthat a protective film is formed even in the area to be polished tothereby extremely lower the polishing rate. Although it has beenattempted to optimize the amount of etching agent or chelating agent inorder to overcome the above-mentioned problem, it is difficult to findout the conditions under which both of the requirements, high polishingrate and less etching and dishing, are met. In addition to this problem,there was also a problem that the results of processes are notreproducible as the results are apt to be influenced by other processconditions. Further, there has been an attempt to obtain a polishingrate of 200 nm/min. or more by mechanically removing the above-mentionedprotecting film under a high polishing pressure of 20 KPa or more(JP-A-2000-252242). However, in the case of porous type low-dielectricconstant type insulating films, which will be widely used hereafter, dueto their low film strength and low adhesiveness to a substrate, anexcessive stress to a substrate causes the peeling and breakage ofinsulating film. Further, when mechanical polishing with a pad iscarried out under an enhanced polishing pressure, the influence of thepad surface becomes greater upon polishing, so that the control of thestate of the pad surface by conventional dressing becomes difficult, andthus the process control becomes more difficult. Further, such atechnique accelerates the consumption of costly pads to increase theprocess cost.

Now, polyoxo acids, particularly heteropoly acid, have high acidity andoxidizing activity, as mentioned in “Chemistry of Poly Acids” (edited byJapanese Chemical Society, published by Gakkai Shuppan Center, August1993), and the use of these substances in the treatment for making ametal into a passive state or an etching treatment of a metal isdescribed in JP-A-9-505111, etc. An example of actual use of aheteropoly acid as an etching agent for a semiconductor surface (AppliedSurface Science, Vol. 135, No. 1/4, pp. 65-70 (1998, 10.8) and anattempt to use a polyoxo acid or its salt as an etching agent forpolishing (JP-A-2000-119639) have been disclosed.

Especially in the latter paper, there are described two embodiments,namely an embodiment of using only polyoxo acid or its salt as anetching agent for polishing (i.e. the first polishing fluid composition)and an embodiment of adding thereto known abrasive grains (i.e. thesecond polishing fluid composition). In the case of the first polishingfluid composition, if a heteropoly acid is used alone as an etchingagent for polishing metallic films, it acts as a liquid oxidant as it issoluble in water. Therefore, both of the above-mentioned tworequirements, i.e. polishing rate and dishing-suppressing performance,cannot be satisfied simultaneously. In other words, if the concentrationof heteropoly acid is increased in order to improve the polishing rate,etching is simultaneously promoted to cause dishing. On the other hand,if a basic substance such as ammonia is added to the heteropoly acid andthe resulting heteropoly acid salt is used, even though the etching maybe suppressed, the polishing rate simultaneously decreases and thepolishing does not progress efficiently. Thus, it has been proposed tomix abrasive particles into the first polishing fluid composition toprepare a second polishing fluid composition for the purpose ofenhancing the polishing rate. However, this provides nothing more thanmechanical polishing by the use of abrasive particles, wherein a highpolishing load is necessary to achieve a high polishing rate.Accordingly, such a technique does not meet the object of the presentinvention which is to achieve a high polishing rate under a low load.

Beside the above, a technique of dispersing abrasive grains in a fluidcontaining heteropoly acid to prepare an aqueous dispersion forchemical-mechanical polishing has also been proposed (EP-A-1123956).However, also in this case, actually, a high polishing load of about 30KPa has to be applied, for achieving a high polishing rate of 300nm/min., while suppressing the etching property causing the dishing.

DISCLOSURE OF THE INVENTION

The object of the present invention is to provide a polishing fluid usedfor polishing a metallic film formed on a semiconductor substrate,characterized by:

-   -   being able to polish a metallic film on a semiconductor        substrate at a high polishing rate even under a low load;    -   being able to control the etching property causing the dishing        to a low level;    -   being able to suppress the occurrence of defects in the polished        surface, such as scratches, erosion (a phenomenon that the        insulating film 2 existing in the peripheral area of metallic        film 4 as in FIG. 1D is polished), etc., as it substantially        does not contain abrasive grains necessary for mechanical        polishing; and    -   further requiring no complicated step of dressing;    -   as well as a method for producing a semiconductor substrate        using said polishing fluid.

The present inventors have conducted extensive studies with the aim ofsolving the above-mentioned problems. As a result, it has been foundthat, if polishing is carried out by the use of a specific polishingfluid for metallic films, the suppression of etching and the highpolishing rate under a low load can be achieved simultaneously, whichhas hitherto been impossible, and that such a polishing method iseffectively applicable also to the metallic films on a fragile poroustype low dielectric constant insulating film substrate. Based on thesefindings, the present invention has been accomplished. Thus, the aspectsof the present invention are as mentioned below.

(1) A polishing fluid for metallic films, the polishing fluid having anetching rate of 10 nm/min. or less, a polishing rate under a load of 10KPa of 200 nm/min. or more, and a contrast ratio of the polishing rateto the etching rate of 20 or more.

(2) A polishing fluid for metallic films, comprising a polyoxo acidand/or a salt thereof, a water-soluble polymer and/or a non-ionicsurfactant, and water.

(3) A polishing fluid for metallic films according to (2), comprising aparticulate composite material consisting of a polyoxo acid and/or asalt thereof and a non-ionic surfactant.

(4) A polishing fluid for metallic films according to any one of (2) to(3), wherein abrasive grains are substantially not contained.

(5) A polishing fluid for metallic films according to any one of (2) to(4), wherein said polyoxo acid and/or a salt thereof is a heteropolyacid and/or a salt thereof.

(6) A polishing fluid for metallic films according to any one of (2) to(5), wherein the HLB of the non-ionic surfactant is 5 to 12.

(7) A polishing fluid for metallic films according to any one of (2) to(6), wherein the non-ionic surfactant is a polyoxyethylene ether of asaturated type higher alcohol having 8 to 24 carbon atoms.

(8) A polishing fluid for metallic films according to any one of (2) to(7), wherein the non-ionic surfactant is a combination of two or morekinds of non-ionic surfactants with different HLBs.

(9) A method for producing a semiconductor substrate comprising a stepof polishing a metallic film formed on the semiconductor substrate,wherein the polishing is carried out with a polishing fluid for metallicfilms according to (1) or (2) under a load of 15 KPa or less.

(10) A method for producing a semiconductor substrate comprising a stepof polishing a metallic film formed on the semiconductor substrate witha polishing stool, wherein the polishing is carried out with a polishingfluid for metallic films according to (1) or (2) at a relative velocitybetween the semiconductor substrate and the polishing stool of 40 m/min.or more.

(11) A method according to (9) or (10), wherein, in the step ofpolishing, the polishing is carried out with a polishing pad notsubjected to a dressing treatment.

(12) A method according to any one of (9) to (11), wherein, in the stepof polishing, the polishing is carried out with a polishing pad havingan average surface roughness (Ra) of 1,000 nm or less on its surface.

(13) A method according to (9) or (10), wherein, in the step ofpolishing, the polishing is carried out with a polishing fluid formetallic films according to (1) or (2) and by a polishing pad containingan inorganic filler.

(14) A method according to any one of (9) to (13), wherein the relativedielectric constant (K) of the insulating film constituting thesemiconductor substrate is 2.5 or less.

(15) A polishing fluid for metallic films according to (1), whereinabrasive grains are substantially not contained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1D are outlined cross-sectional views illustrating examplesof the formation of metallic wirings using the CMP technique.

Hereinbelow, the present invention will be explained more concretely.

As used in the present invention, the term “etching rate” means thethickness of a metallic film which disappears over a certain period oftime, when a substrate with a metallic film formed thereon is immersedin a vigorously stirred polishing fluid. Specifically, a containerhaving an inner diameter of 5 cm is filled with 80 ml of a polishingfluid, and the polishing fluid is stirred at 25,000 rpm by means ofHomogenizer ULTRA-TURRAX T8 manufactured by IKA-WERKE Co. (with shaftS8N-8G). A substrate of Si wafer (15 mm square) having a metallic filmformed thereon is immersed in the polishing fluid under stirring for 3minutes. From the difference in the thicknesses of the metallic filmbefore and after the immersion, the thickness of the metallic filmhaving disappeared per unit period of time is calculated.

As used in the present invention, the term “polishing rate” means thethickness of metallic film which disappears over a certain period oftime, when a semiconductor substrate is polished by a general-purposepolishing apparatus for a semiconductor substrate under predeterminedconditions. Specifically, polishing of a substrate (4″ silicon waferhaving a Cu film with a thickness of 1 μm) is carried out by usingPolishing Apparatus MA-300D manufactured by Musashino Denshi Co. (stooldiameter 300 nm), and using IC-1400 Rodel Nitta Co. (made of foamedpolyurethane) as a polishing pad, under a predetermined load, whilefeeding the polishing fluid at a rate of 50 ml/min., under a conditionthat the relative velocity between the substrate and the polishing stoolis 50 m/min. From the thicknesses of Cu film before and after thepolishing, the thickness of the metallic film having disappeared perunit period of time is calculated.

The present inventors have found that, when a polishing fluid having theabove-standardized properties in specific ranges is used, it is possibleto polish the metallic film on a semiconductor with excellentproperties, such as: that polishing can be carried out under a low loadat a high rate; that the occurrence of defects on the polished surfacesuch as scratches, dishing, erosion, etc. can be suppressed; that theprocess control, such as control of the surface state of the polishingpad, can be simplified; and that the cost of the process can be loweredby reducing the consumption of pads, etc.

First of all, if a polishing fluid having an etching rate of 10 nm/min.or less is used, corrosion of a metal surface can be controlled, so thatthe metal surface is not much roughened at the time of polishing, and nogreat dishing occurs when a substrate having a pattern is polished.

Next, if a polishing rate under a load of 10 KPa is 200 nm/min. or moreand a contrast, i.e. the ratio of the polishing rate/etching rate, is 20or more in a polishing fluid for metallic films, it is possible tofulfil both the improvement of polishing performance, such as preventionof dishing, and the shortening of polishing time simultaneously, both ofwhich are problems to be solved in a CMP process under a condition oflow load.

As polishing fluids having the performance standardized in the presentinvention, polishing fluids comprising polyoxo acid and/or a saltthereof, a water-soluble polymer and/or a nonionic surfactant, and watercan be referred to. The polishing fluids of the present invention maycontain other ingredients, such as usually employed abrasive grains,oxidants and the like, so far as their presence does not disturb theeffect of the present invention or the desired purpose, as will bementioned later. However, the object of the present invention can befundamentally achieved by the above-mentioned ingredients only.Especially, the polishing fluid of the present invention ischaracterized in that it substantially does not contain abrasive grainswhich have been used in the conventional polishing fluids.

The polyoxo acids used in the present invention are the products of thecondensation of an oxygen acid containing Mo, V, W, Ti, Nb, Ta or thelike as a constitutional element. Isopoly acid and heteropoly acidbelong to said polyoxo acid.

“Isopoly acid” means a condensed oxygen acid containing at least one ofthe above-mentioned constitutional elements of polyoxo acids andincludes polymolybdic acid, polyvanadic acid, polytungstic acid,polytitanic acid, polyniobic acid, polytantalic acid, etc. Among theseacids, preferably usable in the present invention for the purpose ofpolishing a metal are polymolybdic acid, polyvanadic acid andpolytungstic acid from the viewpoint of the ability of etching(oxidizing or dissolving) the metal.

“Heteropoly acids” are acids obtained by incorporating a hetero elementinto the above-mentioned isopoly acids as a central element, and areconstituted from a condensed co-ordinated element, a central element andoxygen. Herein, the “condensed co-ordinated element” means theconstitutional element of the above-mentioned polyoxo acids. Aspreferable examples thereof, at least one member selected from the groupconsisting of Mo, W and V can be referred to. In addition to them, Nb,Ta and the like may also be included in the preferable elements. Thecentral element of the heteropoly acid is at least one element selectedfrom the group consisting of P, Si, As, Ge, Ti, Ce, Mn, Ni, Te, I, Co,Cr, Fe, Ga, B, V, Pt, Be and Zn. The atomic ratio between the condensedco-ordinated element and the central element (condensed co-ordinatedelement/central element) is 2.5 to 12.

As concrete examples of the above-mentioned heteropoly acid,phosphomolybdic acid, silicomolybdic acid, phosphovanadomolybdic acid,silicovanadomolybdic acid, phosphotungstomolybdic acid,silicotungstomolybic acid, phosphovanadotungstomolybdic acid,silicovanadotungstomolybdic acid, phosphovanadotungstic acid,silicovanadotungstic acid, phosphomolyboniobic acid, boromolybdic acid,borotungstomolybdic acid, borovanadomolybdic acid, borovanadotungsticacid, cobaltomolybdic acid, cobaltovanadotungstic acid, phosphotungsticacid, silicotungstic acid, phosphovanadic acid, silicovanadic acid, andthe like can be referred to, although these acids are not limitative.

Among the above-mentioned polyoxo acids, preferable are heteropoly acidsfrom the viewpoint of acid strength and oxidizing power sufficient toetch a metal as used for the purpose of polishing; and furtherpreferable are phosphomolybdic acid, silicomolybdic acid, andvanadium-introduced products thereof such as phosphovanadomolybdic acid,silicovanadomolybdic acid, and the like. The polyoxo acids may be usedalone or in the form of a mixture thereof. It is also possible to usethese polyoxo acids in the form of polyoxo acid salts prepared by addinga basic substance to the polyoxo acids, for the purpose of adjusting theacidity of the resulting polishing fluid composition to control thepolishing performance thereof. As the polyoxo acid salt, salts formedbetween the polyoxo acid and a metal, ammonium or an organic amine canbe referred to.

Although the content of polyoxo acid and/or salt thereof in thepolishing fluid of the present invention is not particularly limited, itis preferably 0.1-30% by weight and further preferably 0.5-15% byweight. If the content of polyoxo acid or salt thereof is lower than theabove-mentioned range, it may be difficult to exhibit a sufficientpolishing rate. When said content exceeds the above-mentioned range,there can be observed no conspicuous improvement in polishingperformance brought about by the increment.

The water-soluble polymer used in the present invention includes, but isnot limited to, ethers such as polyethylene glycol, polypropyleneglycol, polyethylene glycol alkyl ether and the like; vinyl polymerssuch as polyvinyl alcohols, polyvinyl pyrrolidone, polyacrolein and thelike; polycarboxylic acids and salts thereof such as polyacrylic acid,polymethacrylic acid, polyacrylamide, polyamic acid, ammonium salts ofpolyacrylic acid, and the like; polysaccharides such as methylcellulose, hydroxypropyl cellulose, carboxymethyl cellulose, celluloseacetate, cellulose nitrate, cellulose sulfate, pectin and the like; andgelatin, starch, albumin etc.

It has been reported that these water-soluble polymers are incorporatedinto a polishing fluid composition as a thickener (JP-A-8-302338) or asa surfactant (JP-A-2000-252242). However, the object of using thewater-soluble polymer in the present invention is different from thoseof this prior art. Thus, in the present invention, a water-solublepolymer is used in combination with the polyoxo acid, by which theprogress of etching can be suppressed and the occurrence of dishing canbe controlled while maintaining a high polishing rate even under a lowload. Among the water-soluble polymers mentioned above, polyethyleneoxide, polyvinylpyrrolidone, polyvinyl alcohol and cellulose derivativesare preferable from the viewpoint of polishing performances, such as thesuppression of etching and the improvement of polishing rate under a lowload, or from the viewpoint of the dispersibility of the formedparticles.

As to the water-soluble polymer to be added, not only the speciesthereof but also the molecular weight thereof markedly affect theperformance of the polishing fluid. Although there is a general tendencythat a higher molecular weight of the water-soluble polymer to be addedgives a higher effect of suppressing the etching, the actual results arequite diverse because the dispersibility of particles and polishing rateare also related, depending on the kind of water-soluble polymer.

The content of the water-soluble polymer in the polishing fluid of thepresent invention is not particularly limited, but varies depending onthe kind of the polymer and the kind and quantity of polyoxo acid orsalt thereof. Preferably, however, it is in the range of 0.01-50% byweight and more preferably 0.05-30% by weight. If its amount is smallerthan the above-mentioned range, sufficient etching-suppressing effectcannot be achieved, and it may be difficult to control the occurrence ofdishing. If its amount exceeds the above-mentioned range, the polishingfluid becomes difficult to handle, because of a rise in viscosity, forexample.

When used in combination with the above-mentioned polyoxo acid, thenon-ionic surfactant of the present invention makes it possible tosuppress the progress of etching while maintaining a high polishing rateunder a low load and thereby suppressing the occurrence of dishing.Surprisingly, this effect is not found when an ionic surfactant such asan anionic or cationic surfactant is used, but is found especiallyremarkably when a non-ionic surfactant, especially a non-ionicsurfactant having an HLB of 5-12 is used. As referred to herein, theterm “HLB” (Hydrophile-Lipophile Balance) is a parameter indicating thehydrophilic character of a surfactant. In the case of the non-ionicsurfactants used in the present invention, this value is in the range offrom 0 to 20. A higher value of HLB means a higher hydrophiliccharacter.

As said non-ionic surfactant, the polyethylene glycol type andpolyhydric alcohol type non-ionic surfactants described in “ShinKaimenkasseizai Nyuumon (Introduction to the New Surfactants)” TakehikoFujimoto, Nov. 1, 1960, published by Sanyo Kasei Kogyo K. K., page 92,Tables 2.5.1, can be used. The polyethylene glycol type non-ionicsurfactants are those prepared by adding ethylene oxide to varioushydrophobic groups to introduce a hydrophilic group into the molecule,and examples thereof include higher alcohol ethylene oxide adducts,alkylphenol ethylene oxide adducts, fatty acid ethylene oxide adducts,polyhydric alcohol fatty acid ester ethylene oxide adducts, higheralkylamine ethylene oxide adducts, fatty acid amide ethylene oxideadducts, fatty oil ethylene oxide adducts, polypropylene glycol ethyleneoxide adducts, and the like. On the other hand, the polyhydric alcoholtype non-ionic surfactants are those prepared by bonding a hydrophilicpolyhydric alcohol to a hydrophobic fatty acid via an ester group or anamide group. Examples thereof include glycerol fatty acid esters,pentaerythritol fatty acid esters, sorbitol fatty acid esters, sorbitanfatty acid esters, sucrose fatty acid esters, alkanolamine fatty acidamides, and the like.

Among the above-mentioned non-ionic surfactants, those having an HLBvalue of 5 to 12 are preferably used in the present invention. If theHLB is smaller than 5, the polishing particles formed have too stronghydrophobicity, which may result in the precipitation of the particlesor a phase separation due to low dispersibility. On the other hand, ifthe HLB is greater than 12, the polishing particles have too highhydrophilicity, which may make it difficult to form the particles and toexhibit the etching-suppressing effect.

The non-ionic surfactants of the present invention are preferably thoseclassified as said polyethylene glycol type surfactants. As examplesthereof, polyoxyethylene ethers of higher alcohols having 8-24 carbonatoms, polyoxyethylene ethers of alkylphenols, and polyoxyethyleneethers of polypropylene glycol (PLURONIC type) can be referred to, amongwhich polyoxyethylene ethers of higher alcohols having 8-24 carbon atomsare especially preferable. The polyoxyethylene ethers of higher alcoholshaving 8-24 carbon atoms can be divided into an unsaturated type havinga carbon-carbon double bond such as an oleyl group in the moleculethereof and a saturated type having no carbon-carbon double bond at all.Because a saturated group does not undergo oxidative deterioration andshows no change in performance over time, polyoxyethylene ethers ofsaturated type higher alcohols are preferable. Examples thereof includepolyoxyethylene decyl ether, polyoxyethylene lauryl ether,polyoxyethylene cetyl ether, polyoxyethylene stearyl ether,polyoxyethylene 2-ethylhexyl ether, polyoxyethylene tridecyl ether,polyoxyethylene isostearyl ether, polyoxyethylene synthetic alcoholether (said synthetic alcohol has 12-15 carbon atoms), and the like.

These non-ionic surfactants may be used alone. However, if two or morekinds of the surfactants different from one another in HLB are used incombination, the excellent properties of the polishing fluid of thepresent invention, namely high dispersibility and low etching propertyof the formed polishing particles, high polishing rate property under alow load, etc. can be exhibited easily. Furthermore, when two or morekinds of non-ionic surfactants different from one another in HLB areused in combination, it is possible to mix together the surfactantspreviously and thereafter mix them with polyoxo acid (or salt thereof)or mix the surfactants simultaneously with polyoxo acid (or saltthereof). Preferably, however, a surfactant having a higher HLB isfirstly mixed with polyoxo acid (or salt thereof) and thereafter thesurfactant having a lower HLB is mixed thereinto. Such a procedure isadvantageous in that a low etching property and high polishing rateproperty under a low load can be exhibited while maintaining a highdispersibility of the formed polishing particles.

In the polishing fluid of the present invention, the content of thenon-ionic surfactant is not particularly limited. Although it may varydepending on the kind of the surfactant used and the kind and amount ofthe polyoxo acid (or salt thereof), the content of the surfactant isusually 0.1-50% by weight and preferably 0.5-25% by weight. If itscontent is smaller than the above-mentioned range, sufficientetching-suppressing effect cannot be exhibited and occurrence of dishingcannot be controlled. If its content is higher than the above-mentionedrange, deterioration in the handling property of the product, such as arise in viscosity, can occur.

The polishing fluid of the present invention is characterized bycomprising a water-soluble polymer and/or a non-ionic surfactant. Inorder to achieve a high polishing rate, however, the use of a non-ionicsurfactant is preferable.

In the polishing fluid of the present invention, water is usually usedas a medium. The dissolution or dispersion of the polyoxo acid (or saltthereof) and the water-soluble polymer and/or the nonionic surfactant isusually carried out by stirring. A process wherein a sufficientdispersion is carried out by the use of a homogenizer, ultrasonic waves,a wet type medium mill, or the like is preferably employed.

Preferably, the thus-prepared polishing fluid is in a highly dispersedstate in water, of a composite material (micelle particles) in whichpolyoxo acid (or a salt thereof) is incorporated into micelles formedfrom a water-soluble polymer and/or a non-ionic surfactant due to aninteraction between the polyoxo acid (or a salt thereof) and thewater-soluble polymer and/or non-ionic surfactant. The case where anon-ionic surfactant is used is especially preferable because theexistence of the non-ionic surfactant facilitates the formation of thecomposite material. The “composite material” referred to hereinfundamentally can be subjected to a particle size measurement by the wettype particle size analyzer and observation of the above structure bymeans of a transmission type electron microscope. It preferably has anumber average particle size in the range of about 10 nm to 1 μm asdetermined by means of a wet type particle size analyzer. Althoughcomposite materials having a number average particle size of smallerthan about 10 nm or composite materials which are so fine that theirparticle size cannot be measured and exist in a highly dispersed stateare also included in the scope of the present invention, such compositematerials are disadvantageous because they generally give a highlyviscous composition. Thus, if workability at the time of polishing istaken into consideration, composite material particles, the particlesize of which is measurable and the structure of which is observable asmentioned above are preferable.

Although the details of the mechanism of polishing with the polishingfluid of the present invention are not clearly known, it is consideredthat the micelle particles formed through the interaction betweenpolyoxo acid (or salt thereof) and water-soluble polymer and/ornon-ionic surfactant act as polishing particles exhibiting a chemicalpolishing action, and can exhibit a high polishing rate even under a lowload while maintaining a low etching rate and suppressing the occurrenceof dishing. As noted above, the polishing particle of the presentinvention is a micelle-form particle, which is essentially different innature from the abrasive grain used for the purpose of mechanicalpolishing. Accordingly, in the present invention, the problems in theconventional mechanical polishing, such as scratches due to coagulatedabrasive grains, the damage to the underlying substrate due to the loadat the time of polishing, etc. can be eliminated.

In the polishing fluid of the present invention, it is also possible touse abrasive grains for the purpose of additionally enhancing thepolishing rate and giving some factors of mechanical polishing, so faras the above-mentioned problems such as scratching, etc. do not occur.However, it is a characteristic feature of the present invention thatthe polishing fluid substantially does not contain abrasive grains. Whenan abrasive grain is used, its content is preferably less than 1% byweight. Examples of the abrasive grain used herein include inorganicparticles such as silicon dioxide, titanium oxide, cerium oxide,aluminum oxide, zirconium oxide, magnesium oxide and the like; organicfine particles such as styrene copolymers, acrylic copolymers, polyvinylchloride, polyacetal, saturated polyester, polyamide, polyimide,polycarbonate, phenoxy resin, polyolefin, olefin copolymers and thelike; and organic particles such as amorphous carbon, carbon black andthe like. Abrasive grains usually used for the purpose of mechanicalpolishing are inorganic particles having high hardness.

Since the polishing fluid of the present invention is very low in theproperty of etching a metallic film, namely the property which causesdishing, it is usually unnecessary to use a protecting film-formingagent with the polishing fluid. However, it is also possible to add acompound that forms a chelate or a complex with a metallic film tofurther suppress the etching, if necessary, as long as the addition ofsuch a compound does not lower the polishing rate substantially.Especially when the metal is copper or a copper alloy consisting mainlyof copper, the addition of benzotriazole or quinaldic acid as achelating agent is effective. As an anti-corrosive agent, in addition tothe above, benzotriazole derivatives such as tolyltriazole,benzotriazolecarboxylic acid and the like, cystine, haloacetic acid,glucose, dodecylmercaptan and the like can be referred to. As to theamount of the anti-corrosive agents used in the present invention, anamount of 100 ppm or less and preferably 50 ppm or less is sufficientfor the purpose, which is much smaller than the amount of anti-corrosiveagent added to the conventional abrasive grains. Inversely, addition ofthe anti-corrosive agent in too large of an amount is undesirable,because it causes a decrease in the polishing rate and makes itimpossible to achieve the desired polishing performance.

Into the polishing fluid of the present invention, a known oxidant maybe incorporated for the purpose of improving the polishing rate ofmetallic film, as long as its addition does not cause excessive etching.As the oxidants which can be incorporated, known oxidants can bereferred to, the examples of which include peroxides such as hydrogenperoxide and the like, perchloric acid, perchloric acid salts, periodicacid, periodic acid salts, persulfuric acid, persulfuric acid salts,nitric acid salts, etc.

According to the need, an acid may be incorporated into the polishingfluid of the present invention. The polishing performance of metallicfilm can be controlled by varying the kind of acid to be added and thepH value of the resulting slurry. As the acid to be incorporated, knowninorganic acids such as sulfuric acid, phosphoric acid, nitric acid andthe like and known organic acids such as oxalic acid, citric acid, malicacid, acetic acid and the like can be referred to.

According to the need, a water-soluble alcohol such as methanol,ethanol, n-propanol, isopropanol, ethylene glycol, glycerin and the likemay be added to the polishing fluid of the present invention.

The polishing fluid prepared in the above-mentioned manner is appliedfor the polishing and flattening of a metallic film formed on asemiconductor substrate. The metallic films on semiconductor substrateto be polished include metallic films for known wirings, plugs, contactmetal layers and barrier metal layers, and the metallic film is composedof a metal selected from the group consisting of aluminum, copper,tungsten, titanium, tantalum, aluminum alloys, copper alloys, titaniumnitride, tantalum nitride and the like. Among the above-mentionedmetals, the present invention is suitably applied to metallic filmscomposed of copper or copper alloys which have low surface hardness andthus are apt to form defects such as scratches, dishing, etc. It is alsopossible, however, to apply the present invention to the polishing ofbarrier metals composed of tantalum or the like.

Upon carrying out the polishing by the use of the polishing fluid of thepresent invention, a polishing method having a special characteristicfeature is employed for fully exhibiting the performance of thepolishing fluid. The present invention also relates to a method forproducing a semiconductor substrate comprising such a polishing step.

The load in the polishing is extremely low, i.e. 15 KPa or less,preferably 10 KPa or less, and more preferably 5 KPa or less. This isfor the reason that, since the polishing fluid of the present inventioncan give a high polishing rate under such a low load, it is unnecessaryto carry out the polishing under a high load as in the conventionalpolishing. As a result, polishing can be carried out without applying anexcessive stress to the substrate, which makes it possible to avoid theproblem of peeling of metallic film due to the breakage of insulatingfilm even in the manufacture of semiconductors with a porous type lowdielectric constant insulating film, which is expected to be introducedand become the main innovation in the near future. Further, when theload during polishing is low, the influence of the pad surface onpolishing is less, which facilitates the troublesome procedure ofcontrolling the pad surface. Further, since the consumption of pads canbe lessened, the process cost can be lowered. Therefore, as noted above,a variety of effects can be expected.

During polishing, the relative velocity between the semiconductorsubstrate and the polishing stool is preferably a high value of 40m/min. or more. That is, even in the case where the factor of mechanicalpolishing is low as in the present invention, a higher polishing ratecan be achieved and thereby the polishing time can be shortened by thecontact between the polishing fluid and substrate at a high velocity.

The polishing fluid for metallic film according to the present inventionhas another characteristic feature in that it makes the dressingtreatment of a polishing pad, which has been essential in the prior art,unnecessary. As referred to herein, the term “dressing treatment” meansa step initially carried out on a polishing pad in the unused stateand/or a step of refreshing the surface of used polishing pads. As tothe dressing in the former meaning, slight dressing is often necessarybecause the existence of foreign material or burrs on the surface of thepad may cause scratch-formation at the time of polishing. However, whenthe polishing fluid of the present invention is used, the dressing inthe latter meaning is unnecessary. That is, in the case of using aconventional polishing fluid containing the usual abrasive grains, thepad surface is finely fluffed by using a disc or a ring-form conditionerinto the surface of which minute diamonds or the like are embedded, sothat the abrasive grains in the slurry are held among the fluffs and adesired polishing rate is exhibited. Accordingly, a periodic control ofthe fluffing state of the pad surface is necessary for avoiding thedeterioration of polishing performance. Further, the conventionalpolishing pad has a foamed structure for the sake of enhancing theholding property of abrasive grains in the slurry. With the progress ofpolishing, abrasive grains are taken into the pores to prevent thesubstitution with fresh abrasive grains to cause a gradual decrease inpolishing rate. For the purpose of preventing this phenomenon, dressingis carried out with the aim of refreshing the surface of the pad. In thecase of the present invention, contrariwise, substantially no abrasivegrains are contained in the polishing fluid, so that no periodicdressing for the purpose of refreshing is necessary. This makes itunnecessary to carry out the troublesome step of dressing, and therebythe production process can be simplified and at the same time theconsumption of costly pads can be suppressed and the process cost can bereduced.

In the method of the present invention, it is recommended to carry outthe polishing with a flat pad having an average surface roughness (Ra)of 1,000 nm or less. According to the prior art, as has been mentionedabove, the surface of the polishing pad is intentionally roughened bythe procedure of dressing in order to achieve a desired polishing rate.However, if polishing is carried out with a pad low in surface flatnessand smoothness, the unevenness on the surface promotes the occurrence ofdishing and makes it impossible to carry out precise polishing. In thecase of the present invention, contrariwise, the desired polishing ratecan be obtained even when polishing is carried out with a pad of veryhigh flatness (Ra is 1,000 nm or less). Accordingly, a precise polishingcan be carried out without reducing the polishing rate.

According to the present invention, it is also possible to carry outpolishing by the use of a pad containing an inorganic filler. Usually, aproduct prepared by foaming an organic polymer, such as polyurethane andthe like, is used as a polishing pad. When a metallic film containingtantalum or a tantalum-containing compound, which are difficult topolish, is to be polished, by the use of the inorganic filler-containingpad, a mechanical factor of polishing is added and the polishing can becarried out with high efficiency. An inorganic filler-containing pad canbe obtained by adding and dispersing a variety of inorganic fillers intoa resin, such as polyurethane or the like, and thereafter forming themixture into the form of a polishing pad. Specifically, the constituentsof a urethane resin, namely an alcohol component such as a diol, polyolor the like and an isocyanate group-containing compound having afunctionality of 2 or more are mixed together and reacted to form aurethane resin. Subsequently, an inorganic filler is added to thethus-obtained resin and kneaded to disperse the inorganic filleruniformly. After forming the uniform mixture thus-obtained into apolishing pad, a crosslinking reaction is carried out by a method ofheat treatment or the like to obtain an inorganic filler-containing pad.As the inorganic fillers which can be used in the present invention,those conventionally used as abrasive grains, as have been mentionedabove, can be referred to. Examples thereof include at least one memberselected from silicon dioxide, titanium oxide, cerium oxide, aluminumoxide, zirconium oxide, chromium oxide, iron oxide, tin oxide, zincoxide, composite metal oxides, metal hydroxides, silicon nitride andtitanium nitride. When these inorganic fillers are added to a pad resin,the surface of the inorganic fillers may be coated with an organicsilicon compound, such as a silane coupling agent or the like, in orderto improve the dispersed state and the affinity at the resin/inorganicfiller interface. As the inorganic filler, those having a particlediameter of 1 nm to 10 μm can be used, and those having a particlediameter of 10 nm to 5 μm are particularly preferable. When the particlediameter is smaller than 1 nm, it is difficult to achieve a sufficientpolishing rate. If the particle diameter is larger than 10 μm, defects,such as scratching and the like, are apt to appear at the time ofpolishing to give an undesirable result. The amount of the inorganicfiller in the constitutional resin is 0.1% by volume to 10% by volume,and preferably 1% by volume to 5% by volume. If the amount of theinorganic filler is too small, the addition of the inorganic filler doesnot exhibit sufficient effect. If the amount thereof is too large,problems arise in the formation of the pad, or the hardness becomes toohigh to cause defects, such as scratching and the like, at the time ofpolishing. As such inorganic filler-containing polishing pad, those thatare prepared by adding cerium oxide to an urethane resin, such as MHCseries manufactured by RODEL NITTA Co., can be used in the presentinvention.

The present invention is particularly effectively applicable to thecases where low dielectric constant insulating film in which theinsulating film constituting a semiconductor substrate has a dielectricconstant (K) of 2.5 or less is used, and particularly the case whereporous type low dielectric constant insulating films which aremechanically fragile are used. That is, in the field of insulatingfilms, it is being studied to make the K value thereof closer to unityas much as possible by giving the films a porous structure byintroducing an air layer into the film. In the case of such a structure,however, the film is generally fragile. In the course of CMP processingof the film, therefore, the insulating film can be broken and peeling ofthe metallic film can take place due to insufficient adhesiveness. Thus,it is necessary to carry out the polishing while minimizing the stressapplied to the substrate. The present invention makes it possible tocarry out the polishing under a low load and thus can satisfy thisrequirement of the process.

Hereinbelow, a method for producing a semiconductor substrate will beexplained concretely.

At first, as shown in FIG. 1A, an insulating film 2 is formed on asemiconductor substrate 1, such as a silicon substrate or the like, andthereafter, trenches for metallic wiring or openings for contact wiringsare formed on the insulating film 2 by photolithography or etching.Subsequently, as shown in FIG. 1B, a barrier metal layer 3 constitutedof titanium nitride (TiN), tantalum nitride (TaN) or the like is formedon the trenches or opening part on the insulating film 2 by sputtering,CVD or the like. Subsequently, as shown in FIG. 1C, metallic film 4 forwiring is embedded so that the thickness thereof becomes higher than theheight of the trenches or openings formed on the insulating film 2.Subsequently, as shown in FIG. 1D, the superfluous metallic film presentin the areas other than the trenches or opening parts are removed by apolishing treatment with the polishing fluid of the present invention.Further, the series of steps mentioned above are repeated as necessary,whereby a semiconductor substrate having a multilevel interconnectionstructure as an electronic part can be obtained. In the production ofthe above-mentioned semiconductor substrate, the polishing of themetallic film on the semiconductor substrate can be carried out byapplying the above-mentioned polishing fluid for metallic films andcarring out the method for producing a semiconductor substrate.

Hereinbelow, the present invention will be explained by reference toexamples. The present invention is by no means limited by theseexamples.

Characteristic properties and polishing performance of a polishing fluidwere evaluated according to the methods mentioned below.

<Measurement of Particle Diameter>

(1) Fine particles (smaller than 5 μm): Measured by a wet type particlesize analyzer (MICROTRAC UPA-9230, manufactured by Nikkisou-sha).

(2) Coarse particles (5 μm or larger): Measured by a wet type particlesize analyzer (LA-700, manufactured by Horiba Seisakusho).

In the descriptions given hereafter, the term “average particlediameter” means a number-average particle diameter.

<Evaluation of Surface Scratch>

A silicon wafer which has been polished in the aforementionedmeasurement of polishing rate is washed and dried, and then the surfaceof the semiconductor wafer was spotlighted in a dark room, and thepresence or absence of one of more scratches is judged by visualobservation.

<Evaluation of Dishing>

By the same method as in the above-mentioned measurement of polishingrate, a 4″ pattern wafer cut out from a 8″ wafer (SKW6-2 specification:oxide film 0.8 μm, TaN 24 nm, Cu 1.5 μm) was polished under a prescribedload, and a line and space part having intervals of 50 μm is measuredwith a desk-top type small-sized probe microscope: Nanopics(manufactured by Seiko Insturuments Co.), to determine the quantity ofdishing on the Cu surface embedded in the space parts. In thisevaluation of dishing, the period of time required for completelypolishing a prescribed film thickness is calculated from the measuredpolishing rate, and a ten percent longer period of time based on thisvalue is used as the polishing time (10% overpolishing).

<Measurement of Pad Surface Roughness (Ra)>

Roughness of pad surface is measured by the use of the desk-top typesmall-sized probe microscope (Nanopics) used in the above-mentioneddishing measurement.

<Polishing Conditions>

The conditions described below are adopted as standard conditions ofpolishing, unless otherwise stated.

-   -   Polishing apparatus: Polishing Apparatus MA-300D, manufactured        by Musashino Denshi Co.    -   Load: 5 KPa    -   Relative velocity between substrate and polishing stool: 50        m/min.    -   Amount of polishing fluid supplied: 50 ml/min.    -   Polishing pad: After fixing IC-1400 (made of foamed        polyurethane) on a polishing stool and dipping it in water, a        treatment is carried out under a load of 20 KPa for one hour by        the use of a 4″ bare silicon wafer, to remove the defects        present on the initial surface of the pad, such as burrs and the        like, after which the substrate is subjected to polishing. The        polishing rate (PR₁₀) used for specifying the polishing fluid        indicates the value under a load of 10 KPa.

The examples shown below are examples of the cases of combining polyoxoacid with a nonionic surfactant.

EXAMPLE 1

As a polyoxo acid, 12 g of phosphovanadomolybdic acid (PVMo, trade namePVM-1-11, manufactured by Nippon Muki Kagku Kogyo-sha), was dissolved in68 g of water. While stirring it with a homogenizer, thereto was added anon-ionic surfactant prepared by mixing 18 g of polyoxyethylene laurylether (SF-1, trade name BLAUNON EL-1503P, HLB=8.3, manufactured by AokiYushi Kogyo-sha) with 102 g of water, to obtain a polishing fluid formetallic film. Characteristic properties of the polishing fluid thusobtained (ER: etching rate, PR₁₀: polishing rate under a load of 10 KPa,contrast: PR₁₀/ER, average particle diameter) and the results ofevaluation of performance under prescribed conditions (PR: polishingrate, quantity of dishing, scratch) are shown in Table 1.

EXAMPLE 2

A polishing fluid for metallic film was prepared in the same manner asin Example 1, except that as the non-ionic surfactant, polyoxyethyleneoleyl ether SF-2 (trade name BLAUNON EN-905, HLB=8.9, manufactured byAoki Yushi Kogyo-sha) was used in place of the SF-1. Results of theevaluation are shown in Table 1.

EXAMPLE 3

A polishing fluid for metallic film containing an anti-corrosive agentwas prepared by adding benzotriazole (BTA) to the polishing fluidcomposition obtained in Example 2 so that the concentration of BTA was50 ppm. Results of the evaluation are shown in Table 1.

EXAMPLE 4

A polishing fluid for metallic film was prepared in the same manner asin Example 1, except that silicomolybdenic acid SiMo (trade name SM,manufactured by Nippon Muki Kagaku Kogyo-sha) was used as the polyoxoacid. Results of the evaluation are shown in Table 1.

EXAMPLE 5

A polishing fluid for metallic film was prepared in the same manner asin Example 1, except that, as the non-ionic surfactant, a mixture of 12g of polyoxyethylene lauryl ether SF-3 (trade name BLAUNON EL-1502.2,HLB=6.3, manufactured by Aoki Yushi Kagaku Kogyo-sha) and 108 g of purewater was used in place of SF-1. Results of the evaluation are shown inTable 1.

EXAMPLE 6

A polishing fluid for metallic film was prepared by dissolving 6 g ofPVMo as a polyoxo acid in 74 g of water, adding thereto a mixture of 6 gof SF-1 as a non-ionic surfactant and 54 g of pure water while stirringthe whole mixture with a homogenizer, and thereafter adding thereto amixture of 6 g of non-ionic surfactant SF-3 and 54 g of water. Resultsof the evaluation are shown in Table 1.

EXAMPLE 7

A polishing fluid for metallic film was prepared by dissolving 12 g ofPVMo as a polyoxo acid in 68 g of water, adding thereto a mixture of 8 gof polyoxyethylene cetyl ether SF-4 (trade name BLAUNON CH-305, HLB=9.4,manufactured by Aoki Yushi Kogyo-sha) as a non-ionic surfactant and 52 gof pure water while stirring the whole mixture with a homogenizer, andthen adding thereto a mixture of 3 g of polyoxyethylene 2-ethylhexylether SF-5 (trade name BLAUNON EH-2, HLB=8.1, manufactured by Aoki YushiKogyo-sha) as a non-ionic surfactant and 57 g of pure water. Results ofthe evaluation are shown in Table 1.

EXAMPLE 8

A polishing fluid for metallic film was prepared in the same manner asin Example 7, except that, as the non-ionic surfactant, polyoxyethylenestearyl ether SF-6 (trade name BLAUNON SR-705, HLB=9.2, manufactured byAoko Yushi Kogyo-sha) was used in place of SF-4. Results of theevaluation are shown in Table 1.

EXAMPLE 9

A polishing fluid for metallic film was prepared by dissolving 12 g ofPVMo as a polyoxo acid in 68 g of water, adding thereto a mixture of 6 gof the above-mentioned non-ionic surfactant SF-4 and 54 g of pure waterwhile stirring the mixture by means of a homogenizer, and subsequentlyadding thereto a mixture of 2 g of polyoxyethylene synthetic alcoholether SF-7 (trade name BLAUNON OX-20, HLB=5.7, manufactured by AokiYushi Kogyo-sha) as a non-ionic surfactant and 58 g of water. Results ofthe evaluation are shown in Table 1.

EXAMPLE 10

A polishing fluid containing an anti-corrosive agent was prepared byadding benzotriazole (BTA) to the polishing fluid obtained in Example 9,so that the concentration of BTA became 50 ppm. Results of theevaluation of this polishing fluid are shown in Table 1.

EXAMPLE 11

A polishing fluid for metallic film was prepared by dissolving 6 g ofPVMo as a polyoxy acid in 74 g of water, and adding thereto a mixture of24 g of SF-2 as a non-ionic surfactant and 96 g of water while stirringthe mixture by means of a homogenizer. Results of the evaluation areshown in Table 1. The polishing fluid obtained herein was somewhat highin viscosity.

EXAMPLE 12

The polishing performance was evaluated in the same manner as in Example1, except that the load of polishing was increased to 25 KPa. Theresults are shown in Table 1.

EXAMPLE 13

The polishing performance was evaluated in the same manner as in Example1, except that the relative velocity between substrate and polishingstool was lowered to 19 m/min. The results are shown in Table 1.

EXAMPLE 14

A polishing experiment was carried out by the use of the polishing fluidobtained in Example 1, on a substrate prepared by forming a Cu filmhaving a thickness of about 0.8 μm on a methylsilsesquioxane typeinsulating film having a porous structure and having a dielectricconstant of 2.1. The polishing was carried out under a low load of 5 KPain the same manner as in Example 1. Neither peeling nor crack of the Cufilm was observed at all, until the completion of the polishing.

Each of the polishing fluids containing fine particles obtained in theabove-mentioned examples was dropped onto a grid equipped with a carbonsupporting film and subjected to air drying to obtain a microscopic testpiece. The test pieces thus obtained were observed under a transmissiontype electron microscope (HITACHI HF-2000, accelerating voltage 200 KV)to investigate their particle structure. As a result, the existence ofparticles in the form where the polyoxo acid was incorporated into thenon-ionic surfactant was observed. Although the particle size varieddepending on the polishing composition, it ranged from about 20 nm to 50nm, and some particles showed a structure of a coagulated productthereof.

COMPARATIVE EXAMPLE 1

A polishing fluid for metallic film was prepared in the same manner asin Example 1, except that, in place of the non-ionic surfactant, thesame amount of sodium docecylbenzenesulfonate SF-8 which is an anionicsurfactant was used. The polishing fluid obtained herein was a uniformsolution so that particle diameter could not be measured. Results of theevaluation are shown in Table 1.

COMPARATIVE EXAMPLE 2

A polishing fluid for metallic film was prepared in the same manner asin Example 1, except that, in place of the non-ionic surfactant, thesame amount of lauryl trimethylammonium chloride SF-9 which is acationic surfactant was used. Results of the evaluation are shown inTable 1.

COMPARATIVE EXAMPLE 3

As a polyoxo acid, 12 g of phosphovanadomolybdic acid PVMo was dissolvedin 188 g of water, and the resulting solution was used as it was as apolishing fluid for metallic film. Since the polishing fluid obtainedherein contained no surfactant and the like at all, it was a uniformsolution, so that the particle diameter could not be measured. Resultsof the evaluation are shown in Table 1.

COMPARATIVE EXAMPLE 4

As a polyoxo acid salt, 12 g of ammonium phosphomolybdate NPMo((NH₄)₃[PMo₁₂O₄₀], manufactured by Nippon Muki Kagaku-sha) wasthoroughly pulverized, added to 88 g of water and dispersed by means ofa homogenizer. Subsequently, 100 g of colloidal alumina (averageparticle diameter 130 nm, manufactured by Shokubai Kasei-sha) was addedso that the concentration of the abrasive grain in the composition was6%, and the whole mixture was dispersed by means of a homogenizer. Thus,a polishing fluid containing alumina particles as abrasive grains wasobtained. Results of evaluation are shown in Table 1.

COMPARATIVE EXAMPLE 5

A polishing fluid for metallic film was prepared by dissolving 6 g ofcitric acid in 62 g of water, adding thereto a solution of 0.4 g of BTAin 3 g of ethanol, further adding thereto 100 g of colloidal alumina(the same as the above) so that concentration of the abrasive grains inthe polishing fluid was 6%, and finally adding 28 g of aqueous hydrogenperoxide (extra pure grade reagent, 30% aqueous solution). Results ofthe evaluation are shown in Table 1.

COMPARATIVE EXAMPLE 6

A polishing fluid for metallic film was prepared by dissolving 5 g ofphosphovanadomolybdic acid (PVMo) in 195 g of water, adding thereto KOHso that the pH was 3.5 while stirring the mixture by means of ahomogenizer, and further adding colloidal alumina (the same as theabove) so that the concentration of the abrasive grains in the polishingfluid was 3%. Results of the evaluation are shown in Table 1.

COMPARATIVE EXAMPLE 7

The polishing performance was evaluated in the same manner as inComparative Example 6, except that the load of polishing was 30 KPa.

COMPARATIVE EXAMPLE 8

A substrate was formed in the same manner as in Example 13 by forming aCu film having a thickness of about 0.8 μm on a methylsilsesquioxanetype insulating film having a porous structure and having a dielectricconstant of 2.1. This substrate was subjected to a polishing experimentunder the same conditions as in Comparative Example 7. As a result,peeling of the Cu film occurred in the course of polishing.

From the above-mentioned results of the Examples and ComparativeExamples, it is apparent that the polishing fluids of the presentinvention comprising a combination of polyoxo acid and a non-ionicsurfactant exhibit a high polishing rate of 400 nm/min. or more oncopper film under a low load of 5 KPa under the condition of therelative velocity between substrate and polishing stool of 50 m/min.,and that more advantageously prevent defects, such as scratching and thelike, under a lower load. Further, owing to such an advantageouscharacteristic feature, they can be used to polish substrates using aninsulating film made of a fragile porous type low dielectric constantmaterial, without any problem. Although there is a tendency that adecrease in the relative velocity between the substrate and thepolishing stool causes a decrease in polishing rate, the polishing rateis still maintained at a high value of about 300 nm/min.

It is apparent that the polishing fluid of the present inventionexhibits the characteristic effect only when combined with a non-ionicsurfactant, and it cannot exhibit a sufficient effect when combined withan anionic or cationic surfactant. When a polishing fluid comprisingonly heteropoly acid is used, the desired performance cannot beexhibited due to the excessively high etching property. On the otherhand, when it is attempted to suppress the etching property ofheteropoly acid by converting the heteropoly acid into an ammonium orpotassium salt, a decrease in polishing performance occurssimultaneously, and sufficient polishing performance cannot be exhibitedat a low load of 5 KPa even if abrasive grains are added.

The examples presented below are examples of polishing fluid in whichpolyoxo acid and a water-soluble polymer are combined.

EXAMPLE 15

A polishing fluid for metallic film was prepared by dissolving 6 g ofPVMo as a polyoxo acid in 154 g of water, and adding thereto, whilestirring the whole mixture with a homogenizer, an aqueous solutionprepared by dissolving 6 g of polyvinyl pyrrolidone K30: PVP (averagemolecular weight 40,000, manufactured by Wako Junyaku Kogyo K. K.) as awater-soluble polymer in 34 g of water. Results of the evaluation areshown in Table 2.

EXAMPLE 16

A polishing fluid for metallic film was prepared by dissolving 6 g ofPVMo as a polyoxo acid in 114 g of water, and adding thereto, whilestirring the whole mixture with a homogenizer, an aqueous solutionprepared by dissolving 12 g of PVP as a water-soluble polymer in 68 g ofpure water. Results of the evaluation are shown in Table 2.

EXAMPLE 17

A polishing fluid for metallic film was prepared by dissolving 6 g ofPVMo as a polyoxo acid in 62 g of water, and adding thereto, whilestirring the whole mixture with a homogenizer, an aqueous solutionprepared by dissolving 40 g of polyethylene glycol 4000: PEG-1 as awater-soluble polymer (average molecular weight 3,000, manufactured byWako Junyaku Kogyo-sha) in 92 g of pure water. The composition thusobtained formed a uniform solution, so that the particle diameter couldnot be measured. Results of the evaluation are shown in Table 2.

EXAMPLE 18

A polishing fluid for metallic film was prepared by dissolving 6 g ofPVMo as a polyoxo acid in 94 g of water, and adding thereto, whilestirring the whole mixture with a homogenizer, an aqueous solutionprepared by dissolving 30 g of polyethylene glycol 20000: PEG-2 as awater-soluble polymer (average molecular weight 20,000, manufactured byWako Junyaku Kogyo-sha) in 70 g of water. The composition thus obtainedformed a uniform solution, so that the particle diameter could not bemeasured. Results of the evaluation are shown in Table 2.

EXAMPLE 19

A polishing fluid for metallic film was prepared by dissolving 9 g ofPVMo as a polyoxo acid in 123 g of water, adding thereto, while stirringthe mixture with a homogenizer, an aqueous solution prepared bydissolving 15 g of PEG-1 as a water-soluble polymer in 35 g of water,and subsequently adding thereto 18 g of the above-mentioned SF-1 as anon-ionic surfactant. Results of the evaluation are shown in Table 2.

EXAMPLE 20

A polishing fluid for metallic film containing an anti-corrosive agentwas obtained by adding BTA to the polishing composition obtained inExample 18, so that the concentration of BTA was 50 ppm. Results of theevaluation are shown in Table 2.

EXAMPLE 21

A polishing fluid for metallic film was prepared in the same manner asin Example 19, except that, as the non-ionic surfactant, SF-2 was usedin place of the SF-1. Results of the evaluation are shown in Table 2.

EXAMPLE 22

A polishing fluid for metal was prepared by dissolving 6 g of PVMo as apolyoxo acid in 168 g of water, adding thereto, while stirring themixture with a homogenizer, an aqueous solution prepared by dissolving 6g of PEG-1 as a water-soluble polymer in 14 g of pure water, andsubsequently adding thereto 6 g of SF-3. Results of the evaluation areshown in Table 2.

EXAMPLE 23

A polishing fluid for metallic film was prepared by dissolving 9 g ofPVMo as a polyoxo acid in 116 g of water and 6 g of ethanol, addingthereto, while stirring the mixture with a homogenizer, an aqueoussolution prepared by dissolving 9 g of PVP as a water-soluble polymer in51 g of pure water, and subsequently adding thereto 9 g of non-ionicsurfactant SF-1. Results of the evaluation are shown in Table 2.

EXAMPLE 24

A polishing fluid for metallic film was prepared by dissolving 12 g ofPVMo as a polyoxo acid in 178 g of water, then adding thereto 6 g of anon-ionic surfactant SF-4 while stirring the mixture by means of ahomogenizer, and then adding thereto an aqueous solution prepared bydissolving 0.4 g of hydroxypropyl cellulose HPC (150-400 mPa.s,manufactured by Wako Junyaku Kogyo K. K.) as a water-soluble polymer in3.6 g of pure water. Results of the evaluation are shown in Table 2.

EXAMPLE 25

Using each of the polishing fluids obtained in Examples 17 and 22, apolishing experiment on a substrate prepared by forming a Cu film havinga thickness of about 0.8 μm on a methylsilsesquioxane type insulatingfilm having a porous structure and having a dilelectric constant of 2.1was carried out. The polishing was carried out under a low load of 5 KPain the same manner as above. As a result, neither peeling nor crack ofthe Cu film was observed at all, until the completion of the polishing.

COMPARATIVE EXAMPLE 9

In 60 g of water were dissolved 6 g of citric acid and 6 g of PVP as awater-soluble polymer. Thereto was added 100 g of colloidal alumina (thesame as above) so that the concentration of the abrasive grain in thecomposition was 6%, and thereto was further added 28 g of aqueoushydrogen peroxide (extra pure grade, 30% aqueous solution). Thus, apolishing fluid for metallic film was obtained. Results of theevaluation are shown in Table 2.

From the results shown in Table 2, it is apparent that, in thecombination of polyoxo acid and a water-soluble polymer also, it ispossible to exhibit a high polishing rate while suppressing the etchingproperty at a low level, similarly to the aforementioned case ofcombination with a non-ionic surfactant. It has also been found that acase of combining polyoxo acid with both water-soluble polymer andnon-ionic surfactant tends to exhibit a relatively higher polishingrate. On the other hand, even if an etching agent other than polyoxoacid is combined with a water-soluble polymer, the etching propertycannot be suppressed, and polishing treatments using such a polishingfluid show a great extent of dishing and have a problem in the polishingperformance.

The examples presented below are for the purpose of evaluating theinfluence of the dressing operation of pads on the polishingperformance.

EXAMPLE 26

In order to assess how the absence of dressing (dressing for refreshingthe pad) influences polishing performance, the polishing fluid used inExample 9 was introduced into a flanged polishing stool in an amountsufficient to immerse a wafer to be polished, and a 4″ dummy wafer waspolished for one hour on the pad. Subsequently, the pad was only lightlywashed with water by the use of a nylon brush, without carrying out anydressing treatment of the pad surface. Then, the polishing performancewas evaluated in the same manner as in Example 9, except that the padobtained herein was used. Surface roughness (Ra) of this pad was 456 nm.The results are shown in Table 3.

EXAMPLE 27

Polishing performance was evaluated in the same manner as in Example 9,except that, as the pad, a non-foamed polishing pad (Ra=120 nm) calledMF Plastic plate with grooves (manufactured by Musashino Denshi-sha) wasused. The results are shown in Table 3.

COMPARATIVE EXAMPLE 10

Prior to polishing, a pad was subjected to dressing for one hour under aload of 3 KPa by the use of a #100 conditioner with embedded diamond.Polishing performance was evaluated in the same manner as in ComparativeExample 5, except that the pad obtained above was used and the polishingload was altered to 30 KPa. The results are shown in Table 3.

COMPARATIVE EXAMPLE 11

The same pad as used in Comparative Example 10 which had undergonedressing was subjected to the same treatment as in Example 26 to obtaina non-refreshed pad. Using this pad, polishing performance was evaluatedin the same manner as in Comparative Example 5, provided that thepolishing load was 30 KPa.

From the results shown in Table 3, it is apparent that the presentinvention gives a polishing performance comparable to that in theinitial case, even if the dressing, which is usually frequently carriedout in the course of polishing for the purpose of refreshing the pad, isnot carried out. Further, it is also apparent that when a pad having avery flat surface is used, an improved dishing property can be obtainedwithout any extreme decrease in polishing rate. Contrariwise, in theconventional polishing fluids containing alumina abrasive grains, thedressing can improve the polishing rate, but the polishing ratedecreases if the dressing for refreshing is not carried out in thecourse of polishing.

EXAMPLE 28

A copper film and a TaN film were polished under a load of 5 KPa by theuse of the polishing fluid prepared according to Example 9 and apolishing pad prepared by pre-treating MH C15A (a pad prepared byincorporating cerium oxide into a urethane resin, manufactured by RODELNITTA Co.) by the use of a #4000 dresser for 10 minutes. As a result,the polishing rate was 580 nm/min. and 80 nm/min., respectively. When athermally oxidized film was polished under the same conditions as above,the polishing rate was about 1 nm/min., demonstrating that polishinghardly progressed. At this time, no scratch was found at all on thepolished surface. Subsequently, using this polishing fluid, a patternedwafer was polished for 3 minutes according to the dishing evaluationmethod, and the quantity of dishing was measured and found to be about70 nm. At this time, it was found that the TaN film in the areas otherthan the trench part could not be detected with a metal film thicknessmeter, demonstrating its disappearance.

COMPARATIVE EXAMPLE 12

A polishing fluid consisting only of polyoxo acid was prepared bydissolving 2 g of PVMo as a polyoxo acid in 198 g of water. Evaluationwas carried out in the same manner as in Example 28, except that thispolishing fluid was used. Thus, when a copper film, a TaN film and athermally oxidized film were polished, the polishing rate was 520nm/min., 30 nm/min. and 1 nm or less, respectively. The etching rate ofcopper film was as large as 110 nm/min. Subsequently, using thispolishing fluid, a pattern wafer was polished to evaluate the dishing.When the polishing was continued for 3 minutes and thereafter thequantity of dishing was measured, a cavity of about 400 nm on theaverage, was formed, and the trench part was in local etched form.

From the results mentioned above, it is apparent that, if polishing iscarried out by the use of the polishing fluid for metallic filmaccording to the present invention and an inorganic filler-containingpolishing pad, polishing of copper film can be carried out at a veryhigh polishing rate of 580 nm/min. even under a extremely low load of 5KPa, and tantalum compounds which have hitherto been difficult to polishcan be polished at a high polishing rate of 80 nm. Further, as in thecase of copper and TaN which are different from each other in polishingrate, both of the materials can be polished in one step whilemaintaining low dishing. This is because the polishing fluid of thepresent invention is characterized by being able to selectively polishthe metallic films only at the site where the pad contacts the metallicfilms under the force greater than a certain level. Even when polishingof copper progresses at a higher rate than on the TaN film, the load iseliminated at the sites where polishing has progressed excessively, andthe polishing at these sites stops at this stage. On the other hand,according to the polishing method of the present invention, silicondioxide film is hardly polished, so that the polishing can be carriedout continuously on a copper film and a barrier film to complete thepolishing on the oxide film. Accordingly, the present invention cangreatly contribute to the simplification of the semiconductormanufacturing process which involves a complicated CMP process. TABLE 1Properties of Polishing polishing fluid Conditions of polishingperformance ER (nm/min.) PR₁₀(nm/min.) Contrast PR/ER Average particlediameter (nm) Load (KPa) Relative velocity (m/min.)

Ra (nm) PR (nm/min.) Quality of dishing (nm)

Ex. 1 6 600 100 30 5 50 x 482 570 69 x Ex. 2 7 600 86 40 5 50 x 482 58075 x Ex. 3 0.9 570 630 40 5 50 x 482 550 48 x Ex. 4 5 580 120 30 5 50 x482 560 73 x Ex. 5 0.9 460 510 140 5 50 x 482 450 50 x Ex. 6 4 530 130100 5 50 x 482 480 70 x Ex. 7 6 560 93 370 5 50 x 482 540 68 x Ex. 8 7560 80 360 5 50 x 482 530 66 x Ex. 9 5 570 110 160 5 50 x 482 550 64 xEx. 10 0.8 530 660 160 5 50 x 482 500 41 x Ex. 11 3 450 150 7 5 50 x 482420 55 x Ex. 12 6 600 100 30 25 50 x 482 620 75 Slightly ∘ Ex. 13 6 600100 30 5 19 x 482 280 96 x Comp. Ex. 1 530 660 1.2 — 5 50 x 482570 >1200 x Comp. Ex. 2 23 540 23 10000 5 50 x 482 480 266 ∘ Comp. Ex. 3560 680 1.2 — 5 50 x 482 580 >1200 x Comp. Ex. 4 4 112 28 160 5 50 x 48250 103 x Comp. Ex. 5 1.2 60 50 150 5 50 x 482 35 55 ∘ Comp. Ex. 6 3 11063 180 5 50 x 482 60 73 ∘ Comp. Ex. 7 3 110 63 180 30 50 x 482 290 98 ∘

TABLE 2 Properties of Polishing polishing fluid Conditions of polishingperformance ER (nm/min.) PR₁₀(nm/min.) Contrast PR/ER Average particlediameter (nm) Load (KPa) Relative velocity (m/min.)

Ra (nm) PR (nm/min.) Quality of dishing (nm)

Ex. 15 2 440 220 700 5 50 x 482 420 58 x Ex. 16 0.7 420 600 10 5 50 x482 410 49 x Ex. 17 4 490 120 — 5 50 x 482 470 60 x Ex. 18 3 460 150 — 550 x 482 440 59 x Ex. 19 6 550 92 70 5 50 x 482 520 61 x Ex. 20 0.9 500560 70 5 50 x 482 490 65 x Ex. 21 8 590 74 150 5 50 x 482 570 66 x Ex.22 1 590 590 120 5 50 x 482 580 71 x Ex. 23 0.7 430 610 300 5 50 x 482420 52 x Ex. 24 9 650 72 320 5 50 x 482 630 83 x Comp. Ex. 9 480 630 1.3150 5 50 x 482 600 >1200 x

TABLE 3 Properties of Polishing polishing fluid Conditions of polishingperformance ER (nm/min.) PR₁₀(nm/min.) Contrast PR/ER Average particlediameter (nm) Load (KPa) Relative velocity (m/min.)

Ra (nm) PR (nm/min.) Quality of dishing (nm)

Ex. 26 5 570 110 160 5 50 x 456 540 65 x Ex. 27 5 570 110 160 5 50 x 120530 49 x Comp. Ex. 1.2 60 50 150 30 50 ∘ 2660 530 122 Slightly o 10Comp. Ex. 1.2 60 50 150 30 50 ∘ 630 230 74 o 11

INDUSTRIAL APPLICABILITY

If the polishing fluid for metallic films according to the presentinvention is used, it becomes possible to suppress the etching anddishing and, at the same time, to polish a metallic film, such as copperfilm and the like, at a high polishing rate even under a low load. Thus,the polishing fluid of the present invention is effectively usedparticularly for polishing a metallic film present on a fragilesubstrate, such as a porous type low dielectric constant insulating filmsubstrate and the like. Further, since the present invention makes itunnecessary to carry out the troublesome step of dressing of the pad, agreat simplification of the process becomes possible. As above, thepresent invention relates to a material having very useful performancesin the polishing of metallic films formed on a semiconductor substrate,so that it has a very high industrial applicability.

1. A polishing fluid for metallic films, the polishing fluid having anetching rate of 10 nm/min. or less, a polishing rate under a load of 10KPa of 200 nm/min. or more, and a contrast ratio of the polishing rateto the etching rate of 20 or more.
 2. A polishing fluid for metallicfilms, comprising a polyoxo acid and/or a salt thereof, a water-solublepolymer and/or a non-ionic surfactant, and water.
 3. A polishing fluidfor metallic films according to claim 2, comprising a particulatecomposite material consisting of a polyoxo acid and/or a salt thereofand a non-ionic surfactant.
 4. A polishing fluid for metallic filmsaccording to anyone of claims 2 to 3, wherein abrasive grains aresubstantially not contained.
 5. A polishing fluid for metallic filmsaccording to claim 2 or 3, wherein said polyoxo acid and/or a saltthereof is a heteropoly acid and/or a salt thereof.
 6. A polishing fluidfor metallic films according to claim 2 or 3, wherein the HLB of thenon-ionic surfactant is 5 to
 12. 7. A polishing fluid for metallic filmsaccording to claim 2 or 3, wherein the non ionic surfactant is apolyoxyethylene ether of a saturated type higher alcohol having 8 to 24carbon atoms.
 8. A polishing fluid for metallic films according to claim2 or 3, wherein the non ionic surfactant is a combination of two or morekinds of non-ionic surfactants with different HLBs.
 9. A method forproducing a semiconductor substrate comprising a step of polishing ametallic film formed on the semiconductor substrate, wherein thepolishing is carried out with a polishing fluid for metallic filmsaccording to any one of claims 1 to 3 under a load of 15 KPa or less.10. A method for producing a semiconductor substrate comprising a stepof polishing a metallic film formed on the semiconductor substrate witha polishing stool, wherein the polishing is carried out with a polishingfluid for metallic films according to any one of claims 1 to 3 at arelative velocity between the semiconductor substrate and the polishingstool of 40 m/min. or more.
 11. A method according to claim 9, wherein,in the step of polishing, the polishing is carried out with a polishingpad not subjected to a dressing treatment.
 12. A method according toclaim 9, wherein, in the step of polishing, the polishing is carried outwith a polishing pad having an average surface roughness (Ra) of 1,000nm or less on its surface.
 13. A method according to claim 9, wherein,in the step of polishing, the polishing is carried out with a polishingfluid for metallic films according to any one of claims 1 to 3 and by apolishing pad containing an inorganic filler.
 14. A method according toclaim 9, wherein the relative dielectric constant (K) of the insulatingfilm constituting the semiconductor substrate is 2.5 or less.
 15. Apolishing fluid for metallic films according to claim 1, whereinabrasive grains are substantially not contained.
 16. A method accordingto claim 10, wherein, in the step of polishing, the polishing is carriedout with a polishing pad not subjected to a dressing treatment.
 17. Amethod according to claim 10, wherein, in the step of polishing, thepolishing is carried out with a polishing pad having an average surfaceroughness (Ra) of 1,000 nm or less on its surface.
 18. A methodaccording to claim 10, wherein, in the step of polishing, the polishingis carried out with a polishing fluid for metallic films according toany one of claims 1 to 3 and by a polishing pad containing an inorganicfiller.
 19. A method according to claim 10, wherein the relativedielectric constant (K) of the insulating film constituting thesemiconductor substrate is 2.5 or less.